Wettstein inaugurated the modern method of classification. He used capital Latin letters to identify the uncials. Codex Alexandrinus received the letter "A", Codex Vaticanus – "B", Codex Ephraemi – "C", Codex Bezae – "D", until he arrived at the last letter used by him, "O". Succeeding generations used this pattern, but newly discovered manuscripts soon exhausted the Latin alphabet.[2] As a result, letters of the Greek and Hebrew alphabets began to be used. Tischendorf, for example, assigned the Codex Sinaiticus the Hebrew letter א. Uncial 047 received siglumב1, Uncial 048 received ב2, Uncial 075 received ג, Codex Macedoniensis – ו, to name a few.[3][4] When Greek and Hebrew letters ran out, Gregory assigned uncials numerals with an initial 0 (to distinguish them from the symbols of minuscule manuscripts). Codex Sinaiticus received the number 01, Alexandrinus – 02, Vaticanus – 03, Ephraemi – 04, etc. The last uncial manuscript known by Gregory received number 0161.[5]Ernst von Dobschütz expanded the number of uncials to 0208 in 1933.[6]

However, the 322 currently catalogued does not provide a precise count of all the New Testament Greek uncials. Uncial 0168 has been lost and over thirty manuscripts are associated with a smaller set of designations.[n 1] Sometimes one number also applies to two separate manuscripts, as with uncial 092a and 092b, 0121a and 0121b, and 0278a and 0278b. Some other numerical designations should be reallocated to other lists: 055 (commentary), 0100 (lectionary), 0129 (lectionary), 0152 (talisman), 0153 (ostracon), 0192 (lectionary), 0195 (lectionary), 0203 (lectionary).[further explanation needed][9] Uncial 0212 from the 3rd or 4th century is more properly a witness to the Diatessaron than to the New Testament itself.[10] So, the number 322 is merely nominal; the actual figure should be somewhat lower.[2][11] Conversely, minuscule 1143, known as Beratinus 2, has some parts that were written in semi-uncial letters.

Content generally only describes sections of the New Testament: Gospels (Gosp), The Acts of the Apostles (Acts), Pauline Epistles (Paul), Catholic epistles (CE), and so on. Sometimes the surviving portion of a codex is so limited that specific books, chapters or even verses can be indicated. Linked articles, where they exist, generally specify content in detail, by verse.

Only one uncial, Codex Sinaiticus has a complete text of the New Testament. Codex Alexandrinus has an almost complete text. It contains all books of the New Testament but lacks some leaves of Matthew (25), John (2), and Second Corinthians (3). Codex Vaticanus lacks the four last books, and the Epistle to the Hebrews is not complete. Codex Ephraemi has approximately 66 per cent of the New Testament. Uncials with designations higher than 046 typically have only one or two leaves.

Some uncials, about 45 of 300, are so often cited as important witnesses to the text of the New Testament that they have not only names, but a single letter code called a siglum, for concise reference in textual apparatus and in academic writing.